As personal computers have come into common use in the home, there has been increasing demand for electronic still cameras which can input image data into a personal computer. The photographic lens for an electronic still camera, however, must have a very short overall length, a sufficiently wide image angle, and so forth, in order to be incorporated into such a camera.
When using conventional CCD arrays for recording images under the VGA standard (having about 350,000 pixels) or the X&A standard (having about 800,000 pixels), the requirements for the photographic lens for such cameras could be met using a relatively simple lens system having a small number of lens elements and no aspherical surfaces. However, recently, electronic still cameras have been introduced having CCD arrays for recording images under the UXGA standard (having 2 million or more pixels). CCD's used for recording images under this standard have a smaller picture element size than previously, and there has been a market trend for the overall size of the CCD array to become larger, as well.
Thus, accompanying the introduction of the UXGA standard, there has been an increase in the resolution required of the photographic lens used with such a camera, as well as a need to provide a large numerical aperture in order to provide a sufficiently bright image so that the amount of light per pixel remains sufficiently high for detection by an individual CCD. Meanwhile, there has been increasing demand for wider-angle lenses in order to keep the overall length of the lens short despite the market trend of the overall size of the CCD array becoming larger.
It has become more and more difficult to provide a sufficiently wide-angle lens for such an electronic still camera while meeting the requirements of a large numerical aperture and high resolution by using a relatively simple lens system made up of a small number of lens elements.